knee pain

Influence of Experimental Knee Pain on Bilateral Loading Patterns during Walking in Healthy Individuals

Purpose: Knee pain is a chief symptom of knee pathology. Both acute and chronic knee pain result in altered joint loads during walking, which potentially result in mechanical and biological changes in knee articular cartilage. Due to confounding factors in clinical knee pain (effusion, muscle weakness, inflammation, structural changes), it is difficult to examine the independent effect of knee pain on walking mechanics. The purpose of this study is to examine whether unilateral experimentally induced knee pain influences bilateral loading patterns during walking in healthy individuals. Methods: This study was a controlled laboratory, cross-over trial. Each of 30 able-bodied subjects (M = 20, F = 10; 23 ± 2.4 yrs, 71 ± 12.7 kg, 178 ± 8.2 cm) completed three experimental sessions: pain (5.0% NaCl infusion), sham (0.9% NaCl infusion), and control (no infusion) in a counterbalanced order, 2 days apart (a washout period). For the experimental sessions, hypertonic (5% NaCl) or isotonic (0.9% NaCl) saline was continuously infused into the right (involved limb) infrapatellar fat pad using a portable infusion pump, which produced a continuous saline flow of 0.154mL/min (total 2.16 mL) for 14 min for the pain or sham session, respectively. No infusion was administered to the control session. Subjects and investigators were blinded regarding the saline solution which was being infused. During each of three experimental sessions, subjects performed 30-sec gait trials at a self-selected speed at two time points (pre- and post-infusion). Ground reaction force (GRF) data were collected using an AMTI instrumented force-sensing tandem treadmill (1200 Hz). The first 4 successful gait cycles in each limb were used for data analysis. A functional data analysis approach (α = .05) was used to detect time (pre- and post-infusion) x limb (involved vs. uninvolved) interactions for the vertical, anterior-posterior, and medial-lateral GRF. Results: Significant time x limb interactions were observed during the pain session (hypertonic saline; 5.0% NaCl; p < .05). Experimental knee pain resulted in up to (i) 0.05 N/kg less vertical GRF and 0.02 N/kg more vertical GRF during various stance phases, (ii) 0.01 N/kg less breaking GRF during loading response, and (iii) 0.007 N/kg less lateral GRF and 0.007 N/kg more lateral GRF during various stance phases in the involved limb. Conclusions: Relative to the pre-infusion condition, subjects during the knee pain condition tended to walk with less vertical, posterior and lateral GRF in the involved limb (painful limb) across various portions of stance, which simultaneously increased loads in the uninvolved limb (non-painful limb). Our data suggest that compensatory loading patterns occur simultaneously for the involved and uninvolved limbs. This unloading pattern in the involved limb may be due to perception of knee pain, which can make subjects feel fear for damaging or provoking pain more during walking. Moreover, voluntary and/or involuntary quadriceps inhibition (e.g., neuromuscular activation and strength) due to experimentally induced knee pain may play a role in reducing the loads in the involved limb because the quadriceps support the center of body mass eccentrically from initial loading response to midstance to prevent collapse of the lower limbs. These asymmetrical loading patterns due to knee pain and associated with neural inhibition may be a risk factor for knee joint disease progression via changes in mechanical components.
Listed In: Biomechanics, Gait


Effects of Transcutaneous Electrical Nerve Stimulation on Gait Kinetics in Individuals with Experimentally Induced Knee Joint Pain

Background: Knee joint pain (KJP) independently alters motor function and gait mechanics, and these alterations may accelerate chronic knee joint disease. While TENS restores motor function deficits, it is unclear whether TENS restores compensatory gait mechanics. The purpose was to examine the effects of KJP on lower-extremity joint moments, and the effects of TENS on the aforementioned variables. We hypothesized that KJP will result in altered gait patterns, and TENS will help restore these mechanical alterations. Methods: We randomly selected 15 subjects for the TENS group, after which subjects were matched for the placebo group. Subjects underwent 3 sessions (hypertonic, isotonic, control). A 20-gauge flexible catheter was inserted into the right infrapatellar fat pad, and an infusion pump infused a saline of 0.154 mL•min¯¹ for 50 min (total = 7.7 mL). A TENS protocol was set at a biphasic mode with 120 µs and 180 Hz for 20 min. To blind placebo treatment, subjects in the placebo group was told that an electrical stimulation had been set to sub-sensory level. High-speed video (240 Hz) and an instrumented treadmill (1200 Hz) were used for gait analysis. Functional analysis of variance were used to evaluate differences between groups over time for joint moments. The mean curve with 95% CIs is represented by polynomial functions, showing us the entire stance, rather than identifying discrete peak points. If 95% CIs did not cross zero, significant difference existed (P < 0.05). Discussion: KJP independently increase internal knee varus moments, which were consistent with previous finding using patients with osteoarthritic knee pain. These compensatory gait patterns may be a result of a pain-avoidance motor deficits strategies. Since observed patterns can create altered mechanical and biological stress patterns on articular surface, it may increase the risk of degenerative knee disease. However, attempting to reduce perceived pain and increase neuron activation through TENS can help overcome deficits in knee and hip joint moments.
Listed In: Biomechanics, Gait, Sports Science